For over thirty years, insulated glass door assemblies for commercial refrigerator and freezer insulations have comprised an insulated glass unit made up of two or more glass panes maintained in spaced-apart relation by tubular spacers with the interior between the panes appropriately sealed. The glass unit in turn is supported within a relatively rugged outer metallic frame, commonly formed from aluminum extrusions, with the metal frame overlapping the periphery of the glass unit for retaining the glass unit in position and for providing a decorative finished appearance to the door assembly. While improvements in energy efficiencies, structural rigidity, and mounting of such door assemblies have taken place over the years, such insulated glass door assemblies have remained substantially unchanged in their outer appearance. Although the desire for style changes has existed, cost considerations usually have prevented product changes.
Because of increasing customer demand for styling changes, manufacturers recently have introduced more modernistic appearing glass door assemblies. These doors have included a single, relatively thick pane that provides the appearance of an all-glass, relatively contemporary, front to the door assembly. While such doors are attractive in appearance, they do not have the efficiency, safety, and durability features the industry has grown to expect in commercial insulated refrigerator door assemblies and have been unable to withstand the relatively abusive use in commercial establishments where doors are repeatedly opened and closed and are frequently struck by shopping carts and the like.
To provide necessary rigidity and durability in conventional refrigerator door assemblies, costly manufacturing procedures heretofore have been required. It is customary to first assemble the insulated glass unit and then fabricate the outer support frame thereon. The latter commonly requires accurate forming of mitered corners of the metal frame members and precision assembly techniques for establishing the necessary squareness. Such fabrication not only is expensive, but unless properly effected, during rigorous use of the door in commercial establishments the components of the frame and glass unit can become separated and destroy the sealed condition to the interior of the glass unit. Moreover, because the outer support frame of such conventional doors is made of metal, it is highly heat conducted and can require electrical heating means for maintaining the portion of the frame exposed to the warmer ambient air at a sufficiently high temperature to prevent condensation build up. Such electrical heating capability not only adds to the manufacturing cost of the door, but increases the operating cost of the refrigeration unit with which the door is used.
Furthermore, in order to maintain the forward glass pane in a frost-free, clear condition, which is essential for aesthetic viewing of merchandise through the door in commercial refrigeration and freezer installations, it is customary to provide a conductive coating on an inside surface of the forward glass pane and to communicate electric current to the coated surface through bus bars mounted on opposite sides thereof. Since the bus bars conduct electric current, it is necessary that they be spaced apart from other possible conductive elements or materials in the glass unit, such as the metallic spacers and carbon containing polyisolbutylene commonly used as the sealant between the spacers and the glass panes. As a result, it has become the practice to position the bus bars on the exposed surface of the forward glass pane inwardly away from the metal spacers a distance of about 1/4 inch. Because the bus bars typically have a width of about 1/4 inch, they not only tend to detract from the aesthetic appearance of the door, but also reduce the unobstructed viewing area through the glass pane by about 1/2 inch on each side.